This invention relates generally to an isolated low voltage switch of the type used to replace conventional wiring associated with wall switches receiving line voltage, and more particularly to a solid state switch located substantially at the point of application of line voltage and operated remotely through low voltage connections.
In the prior art, electro-mechanical AC line switches, are remotely operated by means of an isolated low voltage AC control system. The switch contains a step-down transformer to derive a low voltage control signal from conventional line connections. The switching mechanism is operated by connecting the low voltage AC signal across a heating wire mechanically linked to, but electrically isolated from, the line voltage AC switching element. Heating of the control wire causes contraction thereof and by this motion activates the line voltage switch section.
In one application of the prior art, the device is equivalent to a momentary contact switch wherein the line voltage switch is activated only when the heating element is energized and exerting a constant force on the switch element. In another model two heating elements are used and a mechanical latching mechanism turns the latching AC line switch on or off depending upon which heating element is energized. Parallel momentary contact switch actuators at multiple remote locations are frequently used in such applications. These switches have the advantage in providing easy manual switch control from a multiple of remote locations and ability to use inexpensive, thin wire from the manual actuator locations to the actual switch control which throws the line circuit.
However, there are disadvantages in the prior art systems including reliability problems associated with electro-mechanical switching mechanisms and high manufacturing cost due to individual adjustment and test cycling for each unit. U.S. Pat. No. 2,811,603 shows a device of that type.
What is needed, is a solid state low voltage switch which eliminates the reliability problems inherent in electromechanical switching mechanisms and is economical to produce.